The central purpose of this secondary analysis of the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (NICHD SECCYD) public data sets is to investigate the effects of fathers serving as a routine childcare provider for their young children ("father care"). Although a substantial body of literature has shown benefits of greater father involvement for parenting satisfaction and children's cognitive and social development, it is not clear whether these benefits hold true for young children's experiences with father care as a routine arrangement. Substantial numbers of fathers provide routine childcare arrangement for 13-14% of the children from 6 to 36 months of age, and we have found that more than 65% of its 1364 children (70% of children from two-parent families) received father care as a primary or a supplemental child care arrangement for some amount of time between 1 and 54 months of age. Despite its prevalence, the effects of father care have not been systematically studied. In studies of the effects of different types of childcare, father care is typically lumped with other forms of relative care, and thus not differentiated (e.g. NICHD Early Child Care Research Network [ECCRN], 2004). The NICHD Study of Early Child Care and Youth Development (N=1364, 48% female) provides a unique opportunity for studying differences in children's development associated with variations and their experience of father care as a child care arrangement. Because child care was defined as nonmaternal care in the NICHD SECCYD, and the types and hours of child care experience were collected longitudinally for both primary and supplement arrangements, there is extensive documentation of variations in children's experiences with father care as a type of child care arrangement. In order to address the key question of how and when father care makes a difference for children, the proposed project will address these specific aims: (1) To provide descriptive information about variations in children's father care experiences throughout their preschool years, (2) to investigate multiple predictors of variations in father care from birth through the preschool years, including family demographics, employment conditions, personal characteristics of fathers and mothers, and child characteristics, and (3) To examine the consequences of father care for father-child relationships, mother-child relationships, and children's social and cognitive development into middle childhood.